In manufacturing processes, it is common to move goods from one position to the next by use of conveyor systems having straight or curved conveyor sections. Typically, straight conveyor systems include continuous loop conveyor belts wherein the belts are propelled on a top surface or deck, by a variety of different drive mechanisms, and return on the bottom surface of the conveyor. The belts on curved conveyors are propelled in a similar fashion. However, propelling a continuous belt around a curved section is more complicated than a straight section. This difficulty is exacerbated in a curved conveyor since it is commonly desirable that the curved section(s) be of a small radius, so as to be able to turn at almost a right angle in a confined space.
Curved conveyor belts are therefore typically driven through the use of a linked drive chain, a linkless drive chain, or a drive belt, each of which has a endless loop configuration, and which is driven by an electric motor. The most common way to drive a curved conveyor belt is through the use of a linked drive chain, wherein the drive chain is in the form of a continuous loop, as is the conveyor belt, and is disposed at the outer edge of the conveyor belt or along the middle of the conveyor belt and wherein the drive chain directly drives the conveyor belt. An example of this type of drive mechanism is described in U.S. Pat. No. 6,105,755.
However, these linked drive chain systems can be difficult to operate and maintain, and can require constant adjustment. Also, cleaning of the drive system, when required, can be difficult.
Another method of driving a curved conveyor belt, and more specifically a continuous and unbroken type curved conveyor belt, is to have a portion of the conveyor belt pinched between an external drive wheel and an opposed idler wheel that is spring biased against the drive wheel. As the drive wheel turns, frictional forces are used to drive the conveyor belt. Examples of these types of systems are described in U.S. Pat. Nos. 5,839,570, 5,944,171, 6,564,931, 7,676,741 and 8,167,121.
However, this type of drive mechanism often does not work well because the drive belt is typically driven at only one point along the belt, and the contact between the belt and the drive wheel is by way of friction only. Heavy articles can therefore cause the conveyor belt to slip or lose engagement. Further, where articles such as food products are being conveyed, oils or the like, can become deposited on the conveyor belt, which can potentially cause reduced friction between the drive wheel and the conveyor belt, and causing the belt to slip.
Another drive option is the use of powered rollers or gears which rotate in a plane essentially perpendicular to the belt in order to propel various projections, followers, or linkages, which have been placed on the belt. These types of systems are described in, for example, U.S. Pat. Nos. 4,433,777, 6,843,366 and 8,113,339.
However, prior art attempts to use this approach rely on the use of drive gears configured to rotate in an arrangement wherein the plane of the gear is perpendicular to the belt surface. As such, the gears of these prior art devices are in a plane essentially perpendicular to the plane of the conveyor belt, and thus, the gears have an axis of rotation which is essentially parallel to the belt surface, and, which is also essentially transverse to the belt travel direction.
This type of drive gear is often located at an end of the belt so that the belt loops around the drive gear, but this limits the size of the conveyor belts' end return. For example, a drive gear end roller having a 7.5 cm diameter would cause a significant cleft at the end of the conveyor, where the curved conveyor meets another conveyor. It is highly desirable to minimize such clefts in order to facilitate the smooth transfer of articles from one conveyor to the next conveyor, especially for easily damaged articles. It is therefore preferable to have the end rollers of a curved conveyor as small a diameter as possible, perhaps about 1.5 cm, or even less, which is difficult to accomplish by presently known conveyor systems having a geared end roller which drives the conveyor belt.
Alternatively, the conveyor belt can be driven by a perpendicular gear positioned in the middle of the belt. The perpendicular gear can contact either the top or bottom belt surfaces, but in a preferred approach, the perpendicular gear can be arranged so as to simultaneously contact both the upper and lower belt surfaces. As such, a single gear can simultaneously drive the upper belt in one direction, and the lower belt in an opposite direction.
However, it is essential that constant contact with the perpendicular drive gear be maintained in order to avoid slippage of the belt. In order to facilitate proper meshing of the drive gear and the followers on the belt, the belt must therefore be kept in tension so as to avoid upward (or downward) movement of the belt that would allow the gears to become disengaged with the projections or drive linkages on the belt.
In order to keep the conveyor belt uniformly in tension, and particularly, when employing a curved conveyor, the curved conveyor belt must be manufactured to close tolerances and kept in tension during use, which can be both is difficult and expensive. Moreover, conveyor belts will stretch over time, under such tension, and therefore require frequent adjustment or replacement. As such, this approach is generally undesirable.
It would therefore be advantageous to provide a conveyor belt drive system, and in particular, a curved conveyor belt drive system, which overcame or ameliorated at least one of the problems of the prior art devices and systems. It would further be advantageous to provide a conveyor belt system, and preferably a curved conveyor belt system, which preferably was economical to manufacture, install, adjust, service and/or maintain.